THE MOSAIC DISEASE OF CUCURBITS. 27 
the intensity in healthy and diseased juices after filtration being ap- 
proximately equal. Attempts have been made to precipitate an 
enzym with 45, 70, and 80 per cent alcohol, using the juices of mosaic 
plants filtered through filter paper. The precipitates gave peroxi- 
dase reactions in all cases, but inoculations made with solutions of 
these precipitates were never successful. 
COMPARISON OF CUCURBIT MOSAIC WITH TOBACCO MOSAIC. 
The properties of the virus of cucumber mosaic are strikingly like 
those attributed to the virus of tobacco mosaic, As already indi- 
cated, the symptoms of the two diseases are very similar, as are also 
the changes produced in the anatomy of the respective hosts. Also 
in both hosts the points at which successful inoculations can be made 
correspond with one exception, i. e., in tobacco root inoculations 
produce infection. The vigor of growth and age of the plants are 
important factors in the infection of both hosts. Insects and the 
handling of mosaic and healthy plants in pruning and picking are 
responsible for much of the field transmission of tobacco as well as 
cucumber mosaic. The first symptoms appear in the young leaves, 
both in tobacco and cucumbers, although the virus is found in all 
parts of the stem and leaves, regardless of the development of mosaic 
symptoms. In tobacco the virus is present in the flower parts, in- 
cluding the placental column and integument of the ovule, as is 
shown by Allard (3). It is also present in the mature seeds, accord- 
ing to the same writer. In the case of the cucumber, the virus is 
present in the flower parts and in the immature fruits, but has never 
been found in the mature seed. The vascular system may be con- 
cerned in the distribution of the virus in both cases, at least in the 
writer's opinion, since the evidence on which the theory is based is 
much the same for both hosts. 
The work on the properties and nature of the virus of tobacco 
mosaic has been much more extensive than that on cucumber, and 
furnishes a valuable basis for comparison. The thermal death point 
as worked out by Beiierinck (6), Woods (32), Iwanowski (16), and 
later by Allard (4) seems to lie between 80° and 100° C. This is 
somewhat higher than that of cucumber mosaic, which is rendered 
nonpathogenic if heated above 70° C. The expressed juices of 
mosaic tobacco plants will retain their power of infection for a year, 
or more, in some cases, whether preservatives are used or not, and 
the dried leaves will remain infectious for relatively long periods. 
This is different from the disease on cucumbers, where the expressed 
juices are seldom infectious for more than 48 hours and the dried 
tissues have never proved infectious. 
Disinfectants, such as phenol, formaldehyde, mercuric chlorid, and 
copper sulphate, will destroy the virus in both cases, the virus of 
tobacco mosaic apparently being slightly more resistant in this 
